Method of crystallization and crystallized products



reamed May 3, 1938 UNITEDYSTATES,

METHOD OF CBYSTALLIZATION AND CRYS- TALLIZE D PRODUCTS Chester L. Baker, Berkeley, Calif., assignor to Philadelphia Quartz Company of California, Ltd., Berkeley, Calif., a corporation of California I No Drawing.

Application January 18, 1933, Serial No. 652,418

20 Claims. (01. 23-110) The present invention relates to an improved crystallizing process which is particularly appli-- cable to systems where the solution from which the substance is to be crystallized is of a sticky or syrupy nature and contains an alkali metal silicate. Such solutions though usually supersaturated are difllcult to crystallize. My invention is especially applicable to the production of crystalline hydrates of alkali silicates, although .I wish it to be understood that the principles involved might equally well be used in the produc tion of mixtures of alkali metal silicates with other materials.

1 The invention also relates to certain new products o'r compositions of matter as will further appear.

The invention, to a large extent, has been developed in connection with the production of sodium metasilicate, and the present disclosure,

therefore, will relate in large measure to such material, but, as before stated, it is not-to be limited to this field.

v In the prior art relating to the alkali metal silicates, where crystals, if any, have been produced, they have been contaminated with supercooled vor uncrystalnzed liquid to an extent sumcient to result in an unstable end product which, if ground,

has heretofore tended to agglomerate into a solid the mass as to result in the production of an end product which is substantially free or uncontaminated with supercooled or uncrystallizedmaterial so that in granular or divided condition the product will be stable, dry' and free-flowing and will not tend to agglomerate into solid masses. The new method of promoting crystallization herein disclosed mayalso be used in connection with systems which contain constituents other than those which it is desired to-crystallize, such as soap for example.

More specifically considered, my invention has for its object the provision of an improved process for producing stable hydrates of the alkali metal silicates, notably sodium metasilic'ata. In

my prior applications, Serial No. 465,245, (of which the present application is a continuation in part) filed July 1, 1930, and issued as Patent No. 1,898,707 on February 21, 1933 and Serial No.

551,785, filed'Juiy 18, 1931, I have disclosed certain ways and means for producing stable hydrates of the alkali metal silicates, and the pres ent invention, therefore, is somewhat in the nature of a modification of or improvement upon the processes therein claimed. In this particular held the primary object of the present invention is to produce the desired crystal species by means of a process in which the necessary control is exercised through regulation of the seeding operation without particular control of the temperatures involved. To state the matter in another way, I have now found that if a liquid of the approximate composition of the desired hydrate be templated, cakes and/or masses can be produced in which the conversion from syrupy liquid to crystalline solid is sui'liciently complete to yield end products which are stable and free-flowing even if the crystallization takes place at ordinary ambient temperatures, which temperatures, of

course, are considerably under the melting temperatures of the crystal hydrates involved in the present invention. contemplates and makes possible a marked decrease in the time required to convert the solution into crystal form.

A statement of the more detailed objects of Furthermore, my invention my invention, therefore. may be said to involve (1) the provision of a method for the production of crystalline materials by means of which it is ,or decompose; (2) the provision of a method in which the conversion from syrupy liquid to a crystalline solid is more complete than with previous 1 enormously multiplied so as to bringall portions of the liquid into intimate contact with a focus of crystallization; (4) the provision of a method which results in an end product of flaked character which will remain dry, stable add free-flowwhich will result in considerable saving not only in the cost of manufacture but also in the amount of time necessary to arri ge at the desired end product; (6) the provisionoi' a method in which."

the transition from liquid to solid form' takes place in a much shorter interval of time than has maybe prepared, which mixtures are also stable and substantially free of any tendency to agglomerate; and (8) the production of certain new compositions of matter in stable form. Other objects and advantages will appear hereinafter I or occur to those skilled in the art.

Various examples of the manner in whch my improved method can be carried out are as fol-- lows:

I.Method of producing NazSi0s.5HzO

To 5000 grams of a solution of sodium silicate containing 8.84% NazO- and 28.8% SiO2 are added 1378 grams of caustic soda containing 76% NazO. The solution is then evaporated until the total weight is reduced from 6378 grams to 5090 grams. This hot liquor should test just under 63 B. This solution is allowed to cool to any convenient temperature below 70 C. It is then placed on a roll type ink grinding mill and 500 grams of powdered NazSiOafiHzO crystals added. The mass is then ground on the two primary rolls of the mill for about one minute. The discharge roll is then moved into place and the entire mass discharged onto the knife of the, machine. The product will be white in color and quite opaque. Immediately upon cooling it will become hard and brittle, so that it may be ground into a dry, free-flowing powder. In case the evaporated liquid has been cooled to room temperature, the mass may be discharged from the mill in the form of a very heavy solidifies almost immediately.

' II.Method of Producing NazSiO3.6'HzO To 4525 grams of a solution of silicate of soda containing 8.84% NaaO and 28.8% SiO2 is added 1245 grams of caustic soda containing 76% NazO.

The solution thus formed. is evaporated until the total weight is reduced from 5770 grams to 5000 grams. .The liquid is then allowed to cool to any convenient temperature below 62 C. and

I placed on the two primary rolls of an ink grinding mill. 500 grams of crystalline NazSiOaGI-EO are then added and the mixture ground for one minute. The third roll of the mill is then moved into place and the mass discharged onto the knife of the machine. Upon cooling the mass will become hard and brittle so that it may be ground to a, dry, free-flowing, granular powder consisting of crystalline Na2Si03.6HzO.

III.Method of producing Nazsioaszizo- 1240 grams of caustic soda containing 76% NazO,

and 410 grams of water. The solution is brought to a boil and the small amount of water lost by evaporation replaced, so that the final solution has a weight of 6150 grams. This liquid is cooled to any convenient temperature below 47 C. The mass is then ground for about 1 minute. The third roll of the mill is then moved into place and the entire mass discharged onto the knife of the machine. The discharged mass will be white and creamy in consistency. Upon cooling it will become hard and brittle so that it can be ground'to a dry, free-flowing, granular powder consisting'of crystalline Na2Si03.9H2O.

The foregoingexamples relate to certain of v the sodium metasilicates, but it should be underpaste whichplicable to the production of other alkali metal silicates in stable crystalline form, as well as to mixtures of these with other materials, such, for example, as sodium sesqui-silicate, sodium metaborate (NaBOzAHzO) etc.

By way'of example sodium sesqui-silicate can be produced in the following manner:-

IV.-Meth0d of producing NGaHSiO4.5HzO

To 3300 grams of a solution of silicateof soda containing 8.84% NazO and 28.8% S102 is added 909 grams of caustic soda containing 76% NazO and the solution thus formed evaporated to a weight of 3360 grams. This solution should then test just under 63B. This solution isthen cooled to a temperature of 70 C. or below and 640 grams of caustic soda containing 76% NazO dis solved in it. The solution thus formed is allowed to cool to any convenient temperature below 78 C. and if necessary 500 grams of crystalline Na3HSiO4.5I-I2O mixed in. The mass is then placed on the two primary rolls of an ink grinding roll mill and ground for one minute. The third roll' of the mill is then moved into place and the mass discharged onto the knife of the machine. opaque in color and will almost immediately harden into a brittle mass capable of being ground to a dry free-flowing stable granular powder. More often, however, the mass will be discharged from the machine as thin white flakes which immediately harden and can be used in the arts without further grinding.

In the foregoing example the seeding by the addition of the 500 grams oi crystalline NaaHSlO4.5H'2O may not be necessary because experience has shown that after a period of cooling a number of crystals may sometimes form spontaneously and these can be satisfactorily dispersed by the grinding operation or its equivalent.

My improved process gives rise to an additional and very important advantage in that it makes possible a state 01' more intimate relationship between crystals prepared from solutions which crystallize with difficulty and other substances which modify and/or increase their usefulness.

For example, a mixture of sodium carbonate and the pentahydrate 01' sodium metasilica.e may be made in which the two substances are present, the sodium metasilicate as a crystalline product while the sodium carbonate appears as an amorphous solid, although undoubtedly being finely crystalline. But the two crystals are so intimately interlocked that they appear to the eye or even under a low-power microscope as a homogeneous mass. The same is also true of mixtures of crystalline alkali metal silicates and soap and of salt mixtures where two crystal species are formed concurrently, such as the phosphate silicate mixtures, the silicate metaborate mixtures and the mixtures of the diflerent hydrates of sodium sesquisilicate withthe hydrates of sodium hydroxide. This intimate relationship prevents the possibility of mechanical segregation of the mixed substances and thus safer to use. Some of the silicate compounds are too actively alkaline for certain uses,'as in contact with sensitive fabrics or human skin, and

the presence of hydrates of erties ofthe materials separately.

Insofar as mixtures are concerned, theffollowing examples may be taken as typical methods of procedure:-

V.Method of preparing a mixture of Nda ollzHzO and NG2SiO3.9HzO To 4500 grams of a solution of silicate of soda containing 8.84% NazO and 28.8% S10: is added 1240 grams of caustic soda containing 76% NaaO and 410 grams of water. The solution is brought to a boil and the small amount of water lost by evaporation-replaced so that the final solution has a weight of 6150 grams. This liquid is cooled to any convenient temperature below 47 C. To the liquid is then added 1000 grams of crystalline trisodium phosphate (NaaP0a12HzO) and 500 grams of crystalline NazSiOailI-IzO. The mixture is then placed on the two primary rolls of an ink grinding roll mill and ground for one minute. The third roll is then moved into place and the mass discharged onto the knife of the machine. The discharged material will be white and opaque in color and usually in the form ofthin white flakes which become hard and brit of interlocking crystals of NaaPOalZI-laO and- Na2SiOa.9HzO, said crystals being interlocked during growth, being substantially free from supercooled metastable liquid and being, substantially incapable of mechanical segregation, the composition as a whole being at least 90 per cent crystallized and having substantially no tendency to agglomerate into solid masses.

VI .Method of preparing a mixture of NazCOs and NdzSiOafiHzO NazSlOaSI-IzO crystals are then added and the mixture ground on the two primary rolls of an ink grinding roll mill for about one minute. The third' roll is then moved into place and the material discharged as a heavy, white, opaque paste which solidifies upon cooling, to a hard brittle mass which can be easily ground to dry free-flowing'granular stable powder. The sodium carbonate remains, unchanged during the above procedure and. it occurs in the product in its original state, usually considered amorphous, but known to be finely crystalline. The ground product therefore consists of granules of interlocking crystals of Nil-2C0: and.

in a dry, stable, .non-caking free-flowing state, said crystals being interlocked during growth, being substantially free from' supercooled metastable liquid and being substantially incapable of mechanical segregation, and the NazSiOaM-IaO stable powder.

in the product beingat least 90 per cent crystallized.

VIL-Method of preparing a mixture of soap and NazSiOs.5HzO

To 5000 grams of a solution of sodium silicate containing 8.84% M120 and 28.8% $102 are added 1378 grams of caustic soda containing 76% NazO.

The solution is then evaporated until the total weight is reduced to 5090 grams. The solution is then allowed to cool to any convenient temperature below 70 C. and 500 grams of granulated soap, together with ,500 grams of Na2SlO3.5H2O, added. The mixture is then ground on the two primary rolls of an ink grinding roll mill for one minute. The third roll is then moved into place and the mass discharged as a heavy paste. This mass will harden upon cooling so that it may be ground into a dry free-flowing granular and stable powder.

-VIII.--Method of preparing a. mixture of NazSzOaQHZOT and NaBOzAHzO To'2250 grams of a solution of silicate of soda containing 28.82% S102 and 8.84% NaaO are added 620 grams of caustic soda containing 76% NazO and 630 grams of water. The solution formed is Just brought to aboil and any water lost by evaporation replaced. The solution is then cooled to any convenient temperature below 55 C. At a temperature above 55 C.

NaBOz.4H2O

transforms into NaBOaZI-IzO and since the former compound is desired, it is necessary to maintain the temperature below 55 C. To the solution is then added 1850 grams of borax and 390 grams caustic soda containing'76% No.20. This addition is brought into solution by stirring, care being taken to prevent the temperature rising above 55? C. The massis then placed upon the two primary rolls of an ink grinding roll mill and 100 grams of Na2SiOa.9HzO and 100 grams of NaBO2.4H2O added for seed. The mixture is ground for about one minute and then discharged from the machine as a white, opaque material which solidifies almost immediately to a hard brittle product which whenground will remain dry, free-flowing and stable upon storage. The productwill consist of a definite mixtureof NaBOafiHzO and NazSiOsBHaO.

IX .-Method of preparing a mixture of crystalline 1450 grams oi caustic soda containing 76% NazO are dissolved in5250 grams of a solution of silicate of soda containing 28.84% S102 and 8.84%

NaaO.

The solution thus formed is evaporated to a mill. The third roll is then brought into position and the mass discharged from the machine as a thick white opaque paste which hardens within a short period of time into a brittle mass which can be easily ground to a granular, free-flowing,

Many other mixtures can be made in a similar 7 way providing proper consideration be given to equilibrium characteristics. For example, combinations or penta or monohydrates or sodium sesquisilicate with hydrates oi sodium hydroxide maybe made.

It should also be noted that certain combinations of the hydrates may be produced as stable mixtures, and by way of example I desire to cite the following:-

X.--Method of producing a mixture of NazSiOaSIhO and NGzSiOs.6H2O To 5000 grams of a solution 01' sodium silicate containing 8.84% Nazo and 28.8% S10: are added 1378 grams caustic soda containing 76% NazO. The solution is then evaporated until the total weight has been reduced to 5310 grams. This solution is then allowed to cool to any convenient temperature below 53 C. 250 grams of crystalline NazSiOa.5I-Iz0 together with 25 grams of crystalline NazSiOafiHzO are then stirred in. The mixture is then ground on the two primary rolls oi an ink grinding roll mill for about one minute. The third roll is then moved into place and the of this type is necessary, as other grinding or subdividing machines such as paint mills, colloid I 35 mills or dlsintegrators may very well be employed for accomplishing the same purpose. In iact other expedients may be adopted, within the scope oi this invention, for causing the necessarily thorough and intimate subdivision and distribution of the seed. The factor which is important is to greatly multiply the foci of crystallization by comminuting or subdividing the seed, as by the grinding operation described.

Insofar as my present knowledge is concerned, it would seem that the action involved is a distribution of the seed, together with suflicient multiplication of the loci of crystallization of such nature as will serve to bring substantially all portions of the liquid into intimate contactwith a focus oi crystallization, and this in a reasonably short space of time. The grinding employed in my invention operates to break up, subdivide or comminute the seed and/or the crystals as they are formed so that the whole mass crystallimintothedesiredhydrateinsuchawayasto substantially preclude, in the end product, the firaence of supercooled or uncrystallized mother quor.

The uniform dispersal or distribution of the crystals or crystal fragments may be likened to the distribution of a pigment in a vehicle to form paint. In any event the distribution should be extremely thorough and the number of nuclei should be multiplied to a very great extent in order to obtain the best results.

I I have discovered that the desired result can be brought about by adding seed crystals or the desired hydrate to the uncrystallized solution at room temperature and grinding and dispersing this seed in the solution on an ink grinding roll mill or other grinding device.

Where a roll type rinding mill is employed, such as the ink grinding mill mentioned in the examples, it is possible to produce'an end product of flaky character very similar to corn flakes suchas arecommonly used as a breakfast cereal, except, of course, that these flakes are white. This flaked product or any ground or comminuted form into which the crystallized mass may be converted by suitable mechanical means .will remain dry, stable and free-flowing in storage.

One way in which to determine the degree of transition into crystal form which may result when practicing the foregoing process is to resort to the heat of solution test. It is a fact well known to physical chemists that soluble substances, when dissolved in water, either give oil or absorb heat, and the quantity of heat thus involved is referred to as heat of solution and is expressed in calories per gram molecule. Thus, for example, when one gram molecule of MgSO4.7HzO is dissolved in 400 gram molecules of water, the system "will absorb 3800 gram calories. On the other hand, one gram molecule of MgSO4.H2O will give off 13,300 gram calories and one gram molecule of MgSOr will give off 20,280 gram calories.

- A similar relationship exists between the heats of solution for the various hydrates of the alkali metal silicates, and with particular reference to sodium metasilicate, the values indicated in the following table have been obtained by dissolving, on the one hand, 10 (grams of the crystallized materialin 150 grams of water, and on the other hand, 10 grams of the uncrystallized supercooled liquid in 150 grams of water.

Temperature change when Il grams of material are dissolved in 150 grams of water If one examines the table above he will notice that in the case of NazSiO3.9H2O the uncrystalllzed solution lowers the temperature by 0.55 0., whereas the crystallized material lowers the temperature by 3.48 C. A similar relationship exists in the case of each material. It will thus be seen that if a mixture of crystals and uncrystallized solution of the same chemical composition are used in this experiment a value will be obtained which is less than that given by the uncontaminated crystals. From the values thus obtained it is possible to make a rough calculation of the amount ,of crystalline material in the sample taken. For example: Should the sample taken give a temperature lowering of 2.95, the amount or the crystallized material can be expressed as In the several examples given above heats of solution tests of the character just described indicated that the degree of crystallization was upwards of 90% in every instance and generally f ture at which crystallization takes place.

tion, finely grinding the resulting mixture of crystals and solution while simultaneously disv product. Intimacy of seed distribution should be sufficient to ensure a conversion into crystalline form which will result in a dry, stable, freefiowing end product andyas indicated above, I, prefer to operate in a range which will yield a product which is crystallized substantially 90% or more.

It will be seen, therefore, that I have provided a method for producing crystalline hydrates of s the alkali metal silicates and compositions containing the same in which it is unnecessary to give any particular consideration to the tempera- The stability andcharacter of the end product are determined by suitable control of the seeding step as herein described. The extremely thorough and -intimate manner of seeding the solution which I have described will yield an end product characterized by substantially complete transformation into crystal form. Furthermore, my improved process may be used to produce the various alkali metal silicate crystal hydrates in subto a satisfactory practical and commercial article.

From the foregoing examples it will also be seen that the transition from liquid to crystal form takes place in a much shorter interval of time than has been possible heretofore. This fact lends itself particularly well to application of the invention to continuous manufacturing processes, the economic advantages of which are very material.

I should also like to point out that when the crystals have been comminuted; thus establishing the rapid rate of transition, the mass may be allowed ,to solidify as a film which will produce an end product in the form of flakes, or it may be mechanically atomized to yield a powder directly without grinding or it may be extruded through suitable apertures to yield vermicular particles. In short, the process may be adapted to produce a finished product in any one of a great variety of physical shapes adapted to commercial requirements and all of which are characterized by, the properties of free-flowing and stability. This has not heretofore been possible and results in another advantage, 1. e., with my process the finished article can be produced in particles of predetermined shape and size.

.In practice the advantages of the invention may be realized even in instances where other materials may be added for the purpose of modifying the behavior of the crystals sought. way of example, for detergent or other purposes, materials such as starch, rosin, mineral or vegetable oils, colloidal silicates and/or other agents may be introduced where desired to modify the behavior of the crystal species without departing from the spirit and scope of the present invention.

I claimt- 1. In the production of sodium metasilicatepentahydrate', themethod which includes preparing a solution of the approximate. composi tion of the said hydrate, cooling the solution to any convenient temperature below the melting point of the said hydrate, initiating crystallizapersing the crystals rapidly and uniformly throughout said mixture while said mixture is still in a liquid condition in such manner as to produce a resulting crystallized product substantially free from supercooled liquid and capable of being comminuted to a dry, stable, free-How ing powder.

2. The method er claim 1 wherein crystallization is initiated by seeding with a quantity of sodium metasilicate pentahydrate crystals.

3. In the production of a composition of matter containing a crystalline hydrate of an alkali metal silicate, the method which includes preparation of a solution which corresponds substantially to the composition desired, cooling the solution to any convenient temperature below the melting point of the crystallinehydrate, initiating crystallization thereof, finely grinding the resulting mixture of crystals and solution while simultaneously dispersing the crystals rapidly and uniformly throughout said mixture while said mixture is still in a liquid condition in such manner as to produce a resulting crystallized product substantially free from supercooled liquid and capable of being comminuted to a dry, stabl free-flowing powder.

4. The method of claim 3wherein crystallization. is initiated by seeding with a quantity of the crystalline hydrate desired.

5. The method of making crystalline hydrates of alkali metal silicates which includes preparing a solution substantially corresponding to the composition of a predetermined hydrate, cooling the solution to any convenient temperature below the melting point of the said hydrate, ini- I tiating crystallization, finely grinding the resulting mixture of crystals and solution while simul taneously dispersing the crystals rapidly and uniformly throughout said mixture while said 6. The method of claim 5 wherein crystalliza tion is initiated by seeding with a quantity of the hydrate desired.

[The method of making a definite hydrate of sodium metasilicate which includes preparing a solution approximately corresponding to the composition of the desired hydrate, initiating crystallization, finely grinding the resulting mixture of crystals and solution while simultaneously dispersing the crystals rapidly and uniformly throughout said mixture while said mixture is still in a liquid condition in such manner as to produce a resulting crystallized product substantially free from supercooled liquid and capable of being comminuted to a dry, stable, free-flowing powder.

8. The method of claim 'I wherein crystallization is initiated by seeding with a quantity of the desired hydrate.

9. The method of making a definite hydrate of sodium metasilicate which includes preparing a solution approximately corresponding to the still in a liquid condition in such manner as to produce a resulting crystallized product substantially tree from supercooled liquid and capable of being comminuted to a dry, stable, tree flowing powder.

10. The method of claim 9 wherein crystallisa tion is initiated by seeding with a quantity or the desired hydrate.

11. The method of making a definite hydrate 01' sodium metasilicate which'includes preparing a solution approximately corresponding to the composition of the desired hydrate, initiating crystallization and grinding the mass to subdivide the-crystals in such manner as to distribute fool of crystallization so intimately and rapidly as to result in a dispersal of the order of the distribution of a pigment in a vehicle to form paint, whereby the resulting product is at least 90 per cent crystallized. I

12. The method of claim 11 wherein crystallization is initiated by seeding with a quantity of the desired hydrate.

13. The method of preparing a mixture oi crystalline trisodium phosphate and crystalline sodium metasilicate which consists in preparing a liquid mixture calculated to satisfy the water requirements in the proportions of the two ma- I while simultaneously dispersing the crystals rapidly and uniformly throughout said mixture while said mixture is still in a liquid condition in such manneras to produce a resulting crystallized product substantially free from supercooled liquid and capable of being comminuted to a dry. stable, free-flowing powder.

14. The method of claim 13 wherein crystallization is initiated by seeding with a mixture of crystalline trisodium phosphate and crystalline sodium metasilicate. 4

15. The method of' preparing a mixture of sodi-' um carbonate and sodium metasilicate pentahydrate which consists in preparing a solution of sodium metasilicate pentahydrate, adding sodium carbonate in the desired proportiorninitiating crystallization, finely grinding the-resulting mixture 01' crystals and solution while siimiltaneously dispersing the crystals rapidly and-unii'ormly throughout said mixture while said mixture is still in a liquid condition in such manner as to produce a resulting crystallized product substantially free from supercooled liquid andcapable of being comminuted' to a dry, stable, tree-flowing powder.

16. The method of claim 15 wherein crystallizationis initiated by seeding with crystals of sodium metasilicate pentahydrate.

1'1, In the production of crystalline compositions of matter containing a crystalline hydrate of an alkali metal silicate and another compatible alkali'metal compound, the process which comprises preparing aliquid mixture having a composition substantially corresponding to that of the desired finished product, cooling the liquid mixture to a point below the melting point of the desired crystalline alkali metal silicate, initiating crystallization, finely grinding the mixture of crystals and solution while simultaneously dispersing the crystals rapidly and uniiormly throughout the liquid mixture while said mixture is still in a liquid condition in such manner as to produce a resulting crystallized product substantially free irom supercooled liquid and capable of being comminuted to a dry, non-caking, tree-flowing powder.

18. The method of claim 1'7 wherein crystallization is initiated by the introduction of seed crystals into the liquid mixture.

19. As a new composition of matter, granules of interlocking crystals of an alkali metal silicate hydrate and sodium carbonate in a dry noncaking, free-flowing state, said crystals being substantially free from supercooled metastable liquid and being substantially incapable of mechanical segregation, the alkali metal silicate in said composition being at least 90 per cent crystallized and having substantially no tendency to agglomerate into solid masses.

20. As a new composition of matter, granules oi interlocking crystals of an alkali metal silicute-hydrate and Na:PO4.I2HzO in a dry, noncaking, free-flowing state, said crystals being substantially free from supercooled metastable liquid and being substantially incapable of mechanical ation, the composition as a whole being at least 90 per cent crystallized and having substantially no tendency to agglomerate into solid masses.

- LBAKIR. 

